1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of fabricating a liquid crystal display device, and more particularly, to an array substrate having a color filter on thin film transistor structure and a method of fabricating an array substrate having a color filter on thin film transistor structure.
2. Discussion of the Related Art
In general, since flat panel display devices are thin, light weight, and have low power consumption, they are commonly used in portable devices. Among the various types of flat panel display devices, liquid crystal display (LCD) devices are commonly used in laptop and desktop computer monitors because of their superior resolution, color image display, and display quality.
In the LCD devices, optical anisotropy and polarization properties of liquid crystal molecules are utilized to generate images. The liquid crystal molecules have specific alignment characteristics that can be modified by application of an electric field. Accordingly, due to the optical anisotropy, incident light is refracted according to the alignment of the liquid crystal molecules.
The LCD devices include upper and lower substrates having electrodes that are spaced apart from and face each other, and a liquid crystal material is interposed therebetween. Accordingly, when an electric field is induced to the liquid crystal material when a voltage is supplied to the electrodes of the upper and lower substrates, an alignment direction of the liquid crystal molecules changes in accordance with the supplied voltage. By controlling the supplied voltage, the LCD devices provide various light transmittances in order to display image data.
The LCD devices are commonly incorporated in office automation (OA) devices and video equipment due to their light weight, thin design, and low power consumption. Among the different types of LCD devices, active matrix LCDs (AM-LCDs) have thin film transistors and pixel electrodes arranged in a matrix configuration and offer high resolution and superiority in displaying moving images. A typical LCD panel has an upper substrate, a lower substrate, and a liquid crystal material layer interposed therebetween. The upper substrate, which is commonly referred to as a color filter substrate, includes a common electrode and color filters. The lower substrate, which is commonly referred to as an array substrate, includes switching elements, such as thin film transistors (TFT's), and pixel electrodes.
The operation of an LCD device is based on the principle that the alignment direction of the liquid crystal molecules is dependent upon an induced electric field between the common electrode and the pixel electrode. Accordingly, the liquid crystal molecules function as an optical modulation element having variable optical characteristics that depend upon the polarity of the supplied voltage.
FIG. 1 is a perspective view of a liquid crystal display device according to the related art. In FIG. 1, an LCD device 11 includes an upper substrate 5, which is commonly referred to as a color filter substrate, and a lower substrate 22, which is commonly referred to as an array substrate, having a liquid crystal material layer 14 interposed therebetween. On the upper substrate 5, a black matrix 6 and a color filter layer 8 are formed in a matrix configuration including a plurality of red (R), green (G), and blue (B) color filters surrounded by the black matrix 6. In addition, a common electrode 18 is formed on the upper substrate 5 to cover the color filter layer 8 and the black matrix 6.
On the lower substrate 22, a plurality of thin film transistors T are formed in matrix configuration corresponding to the color filter layer 8. A plurality of crossing gate lines 13 and data lines 15 are perpendicularly positioned such that each TFT T is located adjacent to each intersection of the gate lines 13 and the data lines 15. Furthermore, a plurality of pixel electrodes 17 are formed on a pixel region P defined by the gate lines 13 and the data lines 15 of the lower substrate 22, and the pixel electrodes 17 include a transparent conductive material having high transmissivity, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO).
In FIG. 1, a storage capacitor C is disposed to correspond to each pixel P, and is connected in parallel to each pixel electrode 17. The storage capacitor C is comprised of a portion of the gate line 13 that functions as a first capacitor electrode, a storage metal layer 30 that functions as a second capacitor electrode, and an interposed insulator 16 (in FIG. 2). Since the storage metal layer 30 is connected to the pixel electrode 17 through a contact hole, the storage capacitor C electrically contacts the pixel electrode 17.
In FIG. 1, a scanning signal is supplied to a gate electrode of the thin film transistor T through the gate line 13, and a data signal is supplied to a source electrode of the thin film transistor T through the data line 15. As a result, the liquid crystal molecules of the liquid crystal material layer 14 are aligned and arranged by operation of the thin film transistor T, and incident light passing through the liquid crystal layer 14 is controlled to display an image. For example, the electric fields induced between the pixel and common electrodes 17 and 18 re-arrange the liquid crystal molecules of the liquid crystal material layer 14 so that the incident light can be converted into the desired images in accordance with the induced electric fields.
When fabricating the LCD device 11 of FIG. 1, the upper substrate 5 is aligned with and attached to the lower substrate 22. During this process, the upper substrate 5 may be misaligned with the lower substrate 22, and light leakage may occur in the completed LCD device 11 due to a marginal error in attaching the upper and lower substrate 5 and 22 together.
FIG. 2 is a schematic cross sectional view along II—II of FIG. 1 according to the related art. In FIG. 2, the thin film transistor T is formed on the front surface of the lower substrate 22, and includes a gate electrode 32, an active layer 34, a source electrode 36, and a drain electrode 38. A gate insulation layer 16 is interposed between the gate electrode 32 and the active layer 34 to protect the gate electrode 32 and the gate line 13. As shown in FIG. 1, the gate electrode 32 extends from the gate line 13 and the source electrode 36 extends from the data line 15. All of the gate, source, and drain electrodes 32, 36, and 38 are formed of a metallic material, whereas the active layer 34 is formed of silicon. In addition, a passivation layer 40 is formed on the thin film transistor T for protection. In the pixel region P, the pixel electrode 17 that is formed of a transparent conductive material is disposed on the passivation layer 40 and contacts the drain electrode 38 and the storage metal layer 30.
In FIG. 2, the upper substrate 5 is spaced apart from the lower substrate 22 over the thin film transistor T. On the rear surface of the upper substrate 5, a black matrix 6 is disposed in the position corresponding to the thin film transistor T, the gate line 13 and the data line 15. The black matrix 6 is formed on the entire surface of the upper substrate 5 and has openings corresponding to the pixel electrode 17 of the lower substrate 22, as shown in FIG. 1. The black matrix 6 prevents light leakage in the LCD panel except for the portions for the pixel electrodes 17, and protects the thin film transistor T from the light to prevent generation of photo currents in the thin film transistor T. The color filter layer 8 is formed on the rear surface of the upper substrate 5 to cover the black matrix 6, wherein each of the color filters 8 has one of the red 8a, green 8b, and blue 8b colors and corresponds to one pixel region P where the pixel electrode 17 is located. A common electrode 18 of a transparent conductive material is disposed on the color filter layer 8 over the upper substrate 5.
In FIGS. 1 and 2, the pixel electrode 17 has a one-to-one correspondence with the color filters 8. Furthermore, as shown in FIG. 2, in order to prevent cross-talk between adjacent pixel electrodes 17 and the gate and data lines 13 and 15, the pixel electrodes 17 are spaced apart from the data lines 15 by a distance A and are spaced apart from the gate lines 13 by a distance B. The open spaces A and B between the pixel electrode 17 and the data and gate lines 15 and 13 cause light leakage in the LCD device. For example, the light leakage mainly occurs within the open spaces A and B so that the black matrix 6 formed on the upper substrate 5 should cover those open spaces A and B. However, when arranging the upper substrate 5 with the lower substrate 22 or vice versa, misalignment may occur between the upper substrate 5 and the lower substrate 22. Therefore, the black matrix 6 extends to fully cover those open spaces A and B, such that the black matrix 6 is designed to provide an aligning margin to prevent light leakage. However, when extending the black matrix 6, an aperture ratio of the liquid crystal panel is reduced as much as the aligning margin of the black matrix 6. Moreover, if there are errors in the aligning margin of the black matrix 6, the light leakage still occurs within the open spaces A and B, and deteriorates the image quality of the LCD device.